Thanks, I found it. The file that actually maps Greenstone metadata
to MARC fields is usMARC.c.

> When you have figured everything out, it would be great if you could email
> the list what you were trying to do, and what you had to modify to achieve
> it, and we can add it to our wiki.

We use a custom plugin to import our metadata from XHTML-encoded
<meta> tags. The element naming convention is SCHEMA.Element.qualifier,
e.g. DC.Coverage.spatial. I simply had to change the metadata element
names and types to our names. The goal we are working towards is being
able to search our Greenstone collections from our meta-search portal
(ExLibris' MetaLib).

thanks,
-Don